Froth flotation is a commonly employed process for concentrating minerals from ores. In a flotation process, the ore is crushed and wet ground to obtain a pulp. A frothing agent, usually employed with a collecting agent, is added to the ore to assist in separating valuable minerals from the undesired or gangue portions of the ore in subsequent flotation steps. The pulp is then aerated to produce a froth at the surface thereof and the collector assists the frothing agent in separating the mineral values from the ore by causing the mineral values to adhere to the bubbles formed during this aeration step. The adherence of the mineral values is selectively accomplished so that the portion of the ore not containing mineral values does not adhere to the bubbles. The mineral-bearing froth is collected and further processed to obtain the desired minerals. That portion of the ore which is not carried over with the froth, usually identified as "flotation tailings", is usually not further processed for extraction of mineral values therefrom. The froth flotation process is applicable to ores containing metallic and non-metallic mineral values.
In flotation processes, it is desirable to recover as much mineral values as possible from the ore while effecting the recovery in a selective manner, that is, without carrying over undesirable portions of the ore in the froth.
While a large number of compounds have foam or froth producing properties, frothers widely used in commercial froth flotation operations include polyalkylene glycol compositions and alkyl ethers thereof (see, for example, U.S. Pat. No. 3,595,390; 2,611,485 and 2,695,101). The frothers most widely used in froth flotation operations are compounds containing a non-polar, water-repellant group and a single, polar, water-avid group such as hydroxyl (OH). Typical of this class of frothers are mixed amyl alcohols, methylisobutyl carbinol (MIBC), hexyl and heptyl alcohols, cresols, terpinol, etc. Some effective frothers used commercially are the C.sub.1 -C.sub.4 alkyl ethers of polypropylene glycol, especially the methyl ether and the polypropylene glycols of 140-2100 molecular weight and particularly those in the 400-1100 range.
Although mineral recovery improvements from a preferred frother in the treatment of an ore can be as low as only about 1 percent over other frothers, this small improvement is of great importance economically since commercial operations often handle as much as 50,000 tons of ore daily. With the high throughput rates normally encountered in commercial flotation processes, relatively small improvements in the rate of mineral recovery result in the recovery of additional tons of minerals daily. Obviously, any frother which promotes improved mineral recovery, even though small, is very desirable and can be advantageous in commercial flotation operations, especially in view of increasing energy costs.
It is an object of the present invention to provide frothing agents which improve the selective recovery of mineral values from ores. Further, it is an object of the present invention to provide frothing agents which can be satisfactorily employed in present flotation processes. Further objects of the present invention will become evident in view of the details set forth hereinbelow.
In accordance with the present invention, it has been found that, in a process for collecting mineral values from an ore which comprises mixing ground ore with water to form an ore pulp, aerating said pulp in the presence of a frothing agent, improved recovery results are obtained with sulfide-containing polyalkylene oxide compositions (hereinafter referred to as "frothers") of the formula: EQU H(BO).sub.z (PO).sub.y (EO).sub.x S(EO).sub.x' (PO).sub.y' (BO).sub.z' H
wherein, in said formula, EO = C.sub.2 H.sub.4 O, PO = C.sub.3 H.sub.6 O and BO = C.sub.4 H.sub.8 O, x and x' each are 0-2, y and y' each are 0-7 and z and z' each are 0-2, x+x'+y+y'+z+z' being an average of from 4 to about 14, with the proviso that at least one of x, y or z and at least one of x', y' or z' is always at least 1 and with the further proviso that when y and y' are each 0, one of z or z' is always at least 1.
Those skilled in the art will recognize that, while pure compositions of the frothers herein can be obtained, it is difficult and prohibitively expensive to do so in many instances. Pure or substantially pure compositions as such are useful and within the scope of the present invention; however, reaction product mixtures containing mixed fractions of the same or different alkylene oxide moieties are desirably utilized as they are less costly. Thus, it will be readily apparent to those skilled in the art that the average or average sum of x+x'+y+y'+z+z' refers to the average content of the alkylene oxide moieties per molecule in a given composition. The actual amount of each fraction may be the same or different and the average sum of alkylene oxide moieties per molecule in a given mixture can readily be determined. By way of illustration, a product mixture having an average PO moiety content of about 10 per molecule may be comprised of about equal amounts of frother fractions having average PO moiety contents of 6,10 and 14, respectively.
A preferred embodiment includes product composition mixtures of the above formula wherein z and z' are 0 and the average sum of x+x'+y+y' is from 4 to about 14. In another preferred embodiment, z and z' are 0 and the average sum of x+x'+y+y' is from 4 to about 10. In still another embodiment, z and z' are 0, x+x' is an average sum of 1 to about 4 and y+y' is an average sum of 1 to about 8. Also preferred are mixtures wherein x and x' and z and z' are all 0 and y+y' is an average sum of from 4 to about 14. Additional preferred mixtures are those where x and x' and z and z' are all 0 and y+y' is an average sum of from 4 to about 10. Another preferred class includes mixtures wherein x and x' and z and z' are all 0 and y+y' is an average sum of from 4 to about 8. In an additional preferred embodiment, x and x' and z and z' are all 0 and y+y' is an average sum of 7. In still another embodiment, x and x' and z and z' are all 0 and y+y' is an average sum of 5. Another preferred mixture is where z and z' are zero, x+x' represents an average sum of 2 and y+y' represents an average sum of 4.
The frothers of the present invention are added to the ore and intimately mixed therewith either alone or together with a collector prior to and/or during the flotation step. The ore pulp-frother mixture is then treated under conditions to form a froth. The froth selectively removes the mineral values from the ore and the mineral-rich froth is separated from the ore flotation pulp and recovered. This value-depleted pulp which remains in the flotation cell is removed. The mineral-rich froth is then further treated to recover the desired mineral values. In accordance with the process of this invention it has been found that both the amount of mineral values which are recovered and the concentration of mineral values in the froth are substantially increased over prior processes which employ known frothers. These processing improvements are obtained with substantially the same or lower quantities of frothing agents as compared to those used currently in flotation operations. Accordingly, the present invention provides substantial advantages over prior processes.
The frothers of this invention can be employed in the flotation of metallic and non-metallic ores. Exemplary ores which are processed include sulfides and oxides of copper, molybdenum, lead, zinc, iron, nickel, cobalt, and the like. Such ores may also contain precious metal values. Other exemplary ores are phosphate rock, cement rock, glass sands, feldspars, fluorspars, micas, clays, talcs, coals and ores containing tungsten, manganese, sulfur, and water-soluble minerals such as sodium and potassium chlorides, and the like. The frothers of this invention are employed in amounts of from about 0.005 lbs. per ton ore to about 0.5 lb. per ton of ore; or preferably from about 0.01 lb. per ton ore to about 0.1 lb. per ton ore. Those skilled in the art will recognize that frother amounts will vary depending upon a given plant operation, ore type, etc., and that optimum amounts can readily be determined by mill trial runs. Preferably, the frothers of the present invention are employed in the recovery of copper or molybdenum, most preferably molybdenum.
The frothers of the present invention are prepared by methods known to the art, including block polymer preparation methods.
The frothers employed in the present invention may be prepared according to known methods. For example, the frothers can be prepared by bubbling sufficient quantities of hydrogen sulfide gas through a solution of the polyalkylene oxide reactant, i.e., ethylene oxide, 1,2- and 1,3-propylene oxide and 1,2- or 2,3-butylene oxide or mixtures of these reactants, depending upon the final product desired. The frothers can also be prepared by reacting a mixture from which H.sub.2 S can be generated, e.g., sodium sulfide in methanol, with an ethylene-, propylene- or butylene-chlorohydrin reactant. The reaction is usually carried out in the presence of a catalyst, e.g., sodium or potassium hydroxide, at temperatures ranging from about 50.degree. to about 225.degree. C., and at pressures ranging from ambient to up to about 1000 or more psi. Larger chain, higher molecular weight frothers can also be prepared by further reacting frothers prepared by any of the above with additional quantities of the desired EO, PO or BO reactants and/or mixtures thereof under similar conditions as described. Additions of the EO, PO or BO reactants, including the chlorohydrins, can be carried out sequentially or concurrently with two or more of the reactants being added as a mixture.
The frothers useful in the present invention may best be characterized in terms of their molecular weights. Products of average molecular weight in the range of about 225 to about 950 are suitable for use as frothers with the range of about 250 to about 700 being preferred. The amounts of alkylene oxide or corresponding chlorohydrin reactants necessary to achieve the various compositions within the above-defined formula will be readily apparent to those skilled in the art, who will also recognize that the claim length is based on an average determination of EO, PO and BO moieties present.
The frothers of this invention can be employed either alone or in conjunction with standard frothers and with a conditioning agent or modifier and/or a water-soluble or oily collector or promoter. Suitable water-soluble collectors or promoters which can be employed in the flotation of sulfide or oxide metallic ores are alkali metal xanthates, sodium or potassium ethyl, isopropyl, secondary or isobutyl, amyl, or isoamyl and hexyl xanthates, alkyl thiols, and dithiophosphates such as dicresyl, diethyl, diisopropyl, disecondary or diisobutyl, diamyl or diisoamyl and dihexyl dithiophosphates as free acids or as sodium, potassium or ammonium salts, as well as mercaptobenzothiazole derivatives. Suitable oily collectors which can be employed with the frothers of this invention include dithiocarbamates such as S-allyl-N-ethyldithiocarbamate, S-allyl-N-isopropyldithiocarbamate and S-allyl-N-methyl-dithiocarbamate, as well as allyl/alkyl xanthate esters, dialkyl thionocarbamates and (alkoxycarbonyl)alkyl xanthates; these collectors are oil-soluble.
In the flotation of non-metallic ores, suitable water-soluble and oil-soluble collectors or promoters are oleic acid, crude and refined tall oil, and tall oil fatty acids, naphthenic acids, the sodium, potassium, and ammonium soaps of such acids, black liquor soap, petroleum sulfonates, organic phosphates and polyphosphates, sulfonated oils and fatty acids, sulfosuccinates and sulfosuccinamates. Cationic type collectors such as long chain amines or imidazolines are employed in the flotation of silica and silicates and water-soluble minerals.
Depending on the type of ore treated, conditioning or modifying agents such as alkalies and acids to adjust pH so as to improve selectivity, flotation depressants to inhibit the flotation of unwanted minerals, and activators to enhance flotability and improve flotation rates may be used with the frothers of this invention.